The present invention relates generally to molded, non-metallic, self-retaining bushings; and, more particularly, to improved self-retaining bushings molded from a deformable, resilient, thermoplastic material and which are suitable for usage in a wide range of diverse applications--especially, applications which require adherence to close tolerance inside and outside diameters--viz., tolerances on the order of .+-.0.005" and, in many instances, on the order of only .+-.0.002"--and/or have stringent requirements in terms of sound and/or shock absorbency characteristics. More specifically, the present invention comprises a significant improvement to self-retaining grommets of the type disclosed in U.S. Pat. No. 3,099,057.
While commercially available grommets and similar self-retaining fasteners of the types disclosed in the aforesaid U.S. Pat. No. 3,099,057 have proven to be quite satisfactory for many commercial and industrial applications, they have not generally been found acceptable for usage in applications requiring extremely close tolerances. This has principally been due to the fact that during the molding process for forming such devices, the extremity of the deformable grommet body is flared outwardly, requiring the usage of oversized fastener-receiving holes into which the device is to be inserted. Such oversized holes result in undesired wear and/or chafing problems and undesired noise problems attributable to radial movement of the device in the oversized hole during usage. Moreover, self-retaining grommets of the type disclosed in the aforesaid U.S. Pat. No. 3,099,057 have further found only limited usage in applications requiring either or both of sound absoring and/or shock absorbing characteristics--this due to the limited amount of resilient material that can be employed in the interior of such devices since standard expansion-type tooling employed to "set" the self-locking device is required to pass freely into the interior of the device for purposes of expanding the same.
Thus, in general, self-retaining grommets and similar devices of the type disclosed in the aforesaid U.S. Pat. No. 3,099,057 employ a tubular body portion molded from a suitable thermoplastic material (such, for example, as nylon) with the body portion having an enlarged retaining head at one end and an upsettable, resilient, deformable, flip portion at its opposite extremity which is designed to be expanded outwardly by means of appropriate standard expansion-type tooling inserted into the tubular body portion. During installation the outwardly expanded deformable extremity is caused to flip outwardly and backwardly upon the tubular body about a weakened annular area of reduced wall thickness defined by a groove formed interiorly in the tubular body portion so as to form a second enlarged retaining head disposed on the device and spaced axially from the first integral enlarged retaining head by an axial distance equal to the thickness of the component(s) through which the device is inserted. However, while the two enlarged retaining heads serve to effectively prevent axial movement of the device within the fastener-receiving hole extending through such component(s), the fact that such hole must be oversized to accommodate the outwardly flared extremity of the deformable body portion prior to setting thereof, permits of undesired radial movement within the hole, thereby producing wear and resulting in unwanted noise levels. As a consequence, devices of the type disclosed in the aforesaid U.S. Pat. No. 3,099,957 have generally found acceptance only as grommets, eyelets, liners and the like; and, such devices have not found widespread acceptance as bushings--especially for use in close tolerance applications where clearances between the I.D. of the bushing body and, for example, a rotating shaft extending therethrough, or between the O.D of the bushing body and the structural component(s) within which it is mounted, must be maintained within tolerances ranging from .+-.0.002" to .+-.0.005".